The Study on Chemical Effect of The Water-rock Interaction on The Weathering of Yungang Grottoes

摘要

Yungang Grottoes,at the Southern part of Mount Wuzhou,on the Western suburbs of Datong,Shanxi province of China,extend one kilometer along a mountain cliff.There are 45 eaves left with more than 51,000 statues of various sizes,among which one cave is the largest groups of ancient caves in China.Yungang Grottoes was declared by the State Council of People's Republic of China a national cultural heritage site in 1961,and then entered into the world heritage list in 2001.Much research works have been done to illustrate the source of salts and waters in Yungang Grottoes by geological,hydrological geological investigations and chemical analysis of rain,snow and spring water from Cave 2.Analysis of the chemical compositions and their contents of various rock samples show that the dissolvable salts in grottoes come from the top layer of sandstone strata.This paper discusses the mechanism of water-rock interactions and their possible effects on the quick weathering of the cave rocks with special focus on the function of atmospheric circles.It was found that the rock-water interactions occurred mainly include the dissolution of cementing carbonate and elastic feldspar,the crystallization of salt mineral and the formation and transform of ferric oxides.These reactions facilitate the propagation of cracks in the rock,the lowering of the mechanical strength,the damage of the stone sculptures due to the cyclic freezing-thawing,drying-wetting and dissolution-hydration of salts.